Generator Earthing Types - TN-S or IT?
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- Опубликовано: 31 май 2024
- Earthing systems for generators.
Although an earth electrode may be present, it's not likely to be a TT arrangement.
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Reading the comments, someone really needs to shed some more light on this whole subject. It's a deep rabbit hole.
can you show how to connect a generator switchover supply to supply a house circuit eg a few sockets, 1 lighting circuit & an oil boiler heating as needed after a storm power cut
I’d love to see this too. Especially the earth arrangement for a house that has a TN-C-S supply.
I've been considering this very issue ever since I bought my cheap generator with 110VAC and 230VAC sockets and whether or not to connect the neutral and earth together - since they are not connected internally. I think you've answered a question that I considered: using the earth from my mains supply for the generator earth. I concluded it's not a good idea to connect two systems together in that way and so I've been watching your videos on installing a ground rod instead.
They use IT systems in hospital operating theaters, even the sockets within the theatre
why?
@@lordjaashin More reliable than a TN-system. In a TN system one fault and the circuit is disconnected, in IT it actually requires two faults at the same time to cause a disconnect. But these IT systems are only in small areas, fault finding is a pain. And the bigger the installation is, the more of a pain it becomes to find a fault. In such critical installations like hospitals the insulation is monitored continuously due to this. The first earth fault will turn the IT system into a TN system, the leg with the earth fault will then become the neutral. An additional second fault will cause a disconnection of the circuit.
Interesting video thank you. Your inverter shown at the beginning has an earth contact stud implying it should be earthed. Also what connection relative to that stud does the socket earth pin have?
@@martinwinfield2935 many PSW inverters have this & it must be earthed separately to any metalwork.
I personally wouldn’t pay much attention to this video, I’m not convinced he knows what he’s talking about.
Perfect info for off grid installation. Thank you!
Aaa! In Norway, 3phase IT is the main standard used on the power grid, and supplied to houses. Very few houses actually have a TN connection(and very few only have one or 2 phases, we always supply all 3) We are as advanced as cheap inverters are :-) The minority of houses connected to TT networks are not supplied with neutral wires. Only 3x approx 115V phases. We seem to hate the neutral wire. Good informative video!
Become electrocuted because the neighbor connected a defective appliance with an earth fault to the grid, in such a system the voltage between the other two lines (three-phase, the ones without the fault) and earth potential can go up to 400V...Nice! 🤣 You can avoid this voltage increase, but actually it's not a nice system in case of a fault. One method to avoid it is using a Wye configuration without a neutral.
IT here is only for small areas which require a high reliability, for example hospitals. Insulation must be monitored continuously, fault finding is a pain the bigger the IT grid is. First fault will turn it from IT into TN. And the second fault disconnects the circuit, if the current is high enough...
In Germany it's three-phase too, but the most common systems are TN-C-S and TT. IT only for small areas which require a high reliability, for example hospitals. Insulation must be monitored continuously, fault finding is a pain the bigger the IT grid is. One fault will turn it from IT into TN, and the second fault disconnects the circuit if the current is high enough...
So, 200V appliances is vastly used in Norway?
@@piratedprivacy9052 . We use 230V, but it is a very fluctuating voltage! One day, I might measure 229V, the next I might measure 237, and 240! This applies to several houses. The 230~ voltage is achieved by connecting an appliance to "L1" and "L2 or "L3", not"L" and "N". It's is actually quite similar to the American grid, although we ground the transfomers middle tap, and send both phases to the consumer(top and bottom tap, if I have understood correctly). If I were to probe between a phase and the earth/soil I should measure 115-130V. We do indeed use an earthing system, where every house has a ground-electrode or a bare copper wire running around the house underground. Our 2pole circuitbreakers do by new standards have leakage current detection, and will break the circuit if any current higher than 30mA goes through a human to ground/earth lead to ground. In theory, the fault current should run back to the nearest local transformer that usually supplies the whole village/area. Sometimes, we also supply the earthing all the way from the transformer to the consumer. Our Electricity meters (smart-meters) do in fact measure current and any fault current, and will notify the supplier if there is any fault. They sometimes go completely nuts, and will send an electrician to your house.
Hi John thanks for sharing your video with me and I would love to see a lot more of your videos and also for of tips and ideas
I used to build and service generators, on many older three phase sets sets I would find that there was a big fat earth stud provided on the alternator foot which would be connected to an earth rod but inside the alternator connection box the neutral was not connected to the frame. Some of these units had been running like that for years.
In marine applications the 480VAC 3 phase systems are most likely an IT arrangement. The argument being fault tolerance. A single fault will not create a short, or trip an RCD. There needs to be a ground fault detection system that signals the fault to be isolated when possible, and repaired. Some sort of high impedance coupling to vessels hull must exist to prevent the IT grid from charging up like a capacitor, carrying many kV if no measures were taken. IT earthing is quite tricky to get right.
Hello, very explained as per usual!
Very interesting! In computer UPSes I've used they say the output neutral and earth is referenced to the battery negative terminal, but they also advise against unplugging the unit from the mains while the inverter is running as they say it can cause the output to float, so I guess this means they are internally connecting the input earth to the output earth? These devices are designed to power multiple pieces of equipment though, some of which might be connected (via signal cables with ground wires) to other equipment running on alternate power feeds (generators, redundant feed from a different grid transformer, etc.) so I guess they have no choice but to tie all the earths together.
Exactly, the smaller UPSes rely on the mains cable for their earth reference entirely, so you might cause equipment damage if you remove the incoming feed while it’s powering something that’s grounded through some other path, like a server rack. Some larger UPSes are designed to cope with this, as you might have a neutral fault upstream and loose the bond between the neutral and earth, or you have a generator that breaks the neutral as well as the phases when switching over. It’d be interesting to see how they cope with it, as they can also recover from that fault when the mains returns and sync back to the grid after free running for some time, presumably by running the frequency up or down slightly to catch up to the grid.
@@sstorholm Interesting, I hadn't thought about how they might cope with a broken neutral. I'm not sure they bother syncing back to the grid though. They usually mention somewhere how long the switchover delay is when the inverter starts up. I measured it a few years ago on a small consumer UPS and the output had no power for about 200ms during the switchover. I think once the power comes back on they just switch back to the grid and you get another ~200ms gap in mains power on the connected equipment. For stuff that can't cope with even that short interruption, you'd go for the dual-conversion units that run the inverter all the time, even when grid power is available.
@@Berkeloid0 I was speaking of larger units running in dual conversion mode, the resync is important since they are usually equipped with an external make before break bypass switch, so it’s rather important that the input and output are in sync, otherwise you might get a bit of a fireworks display when the bypass is thrown.
@@sstorholm That must be unique to very large units, consumer units just have a couple of relays that are timed to do break-before-make on the bypass. I guess they assume any equipment that critical will have more than one power feed so the slight interruption in the rare case of a fault or maintenance can be accommodated. They also come with strong warnings not to connect grid power on the output.
I wonder what happens to the units you are talking about if the bypass is operated during a power outage. Presumably then the UPS may not realise and could cause issues when the power comes back on again, unless operating the bypass informs the UPS and switches off the inverter if there is no grid waveform to sync to?
wow, nice video, straight to the point and clear!!
John, ? What type of battery supplied generator would be recommended for modern gas boilers. ? What extra features are required in addition to pure sine wave.
Hi John,
You missed out the T part of IT on your drawing which is met by connecting an earth electrode to conductive parts.
Within rail and hospitals IT earthing is used extensively with earth electrodes and plenty of class 1 equipment.
Hi John, thanks for this video. Why there is an earth connector on the outside of the housing of the small inverter (the inverter at the very beginning of your video)? Because if I would connect it to earth, there is still no connection to one of the two live wires to define one of both as neutral with earth potential, right? So anyway there cannot be a flow back to the power source through this housing connector? I don´t get it. Maybe you can help?
great video John, especially for offgriders
Hi John on a domestic installation single phase tncs supply do you break the neutral in a change over switch or does it not matter as earth and neutral are neutralised at the supply authorities meter anyway
Could y do a video on the dark arts of shore to ship and ship to shore power systems?
I'm not including the accidents when a ship runs into a powerline in the Straits of Messina or similar circumstances.
thanks John, very helpful
Good 👍 job for covering this. have to fit solar equipment and it has a ups output issue comes when house is TNCs and inverter becomes its own power supply for the house 💪 😀..fun fun fun.
Hi, I have a manual dexterity test at national grid for substation craftsperson apprentice, I will have take something apart then put jt back together. What do u guys reckon it will be?
@ JW,
Thanks for explaining this, I don't do a lot of generator work as a rule, but when you read our standards over here pertaining to generator installation (after you've bought them) they are full of lawyer-speak and no real help.
Every generator I've ever been a part of installing, has been totally different, could be stand-alone 3 phase, portable single phase.
When you go to permanently wire a generator into a switchboard, with a manual transfer switch, I insist on there being a flexible cable from the generator to an appliance inlet (this is a reverse plug, as in it has pins, the connector has the socket arrangement), this has caused so many issues with home-owners wanting the thing hooked up cheaply.
The bit that always confused me, was if you would use a seperate Earth Electrode, if the generator was feeding say an out-building (garage) that was supplied from the house, in this situation, I don't think I've ever seen an Earth Electrode driven beside the generator?
Maybe them installs have been done wrong?
Here in North America, rather than a single L1 at 230V, on a 240V generator we have two legs of opposite polarity at 120V each to ground. In that situation the neutral tap comes off the middle of the coil, with L1 and L2 at opposite ends. Of course the polarity of L1 and L2 are 180 degrees apart. The ground is bonded to the middle neutral tap, which explains why some generators built for North America won't be optimally designed for a single 230 V system like used in the UK. I wouldn't necessarily call it shoddy manufacturing, just a different system. In the North American system the downstream consumer can have either 240 V between the two opposite legs or 120V to neutral on either side. In a big circuit panel there is some effort made to balance the usage of the two legs so the common neutral only carries the difference between the two back to the transformer.
Can you expand on the "with the exception of certain types of gas boilers" please? I imagine the principal use of a small inverter for a lot of people will be to keep the central heating running in a power cut...
Some gas boilers have been reported to not work when connected to an isolated supply from an inverter. It's probably to do with the flame sensing circuit, which uses flame rectification.
Boilers use a particular way to sense the presence of a flame, they rely on a small current between live and earth, that is conducted by the flame. Thus they require not only that the live supply is referenced to real earth, but also they mind polarity, if you invert L and N the boiler doesn't work. For example it happened to a person that I know that the boiler stopped working, then I checked and L and N were swapped by the supply company by mistake. Also in my country in some areas it's still in place an old supply that is 220v 3 phase, meaning that to get 230v you have to get 2 phases, and thus around 110v L to E. In that supply boilers can have problems, and that cases you have to install an isolation transformers just to have 220v L to N, connecting the N of the secondary of the transformer to E.
@@jwflame This form of flame supervision becomes an issue when the supply polarity is reversed.
@@alerighi How does that not trigger an RCD is the current less than 30mA?
JW : "IT" needs earthing....
Me : what part of "it"?
JW : we need a video to describe IT!
Got a question regarding the grounding bolt on your inverter. If you ground the inverter from this bolt to the ground of a house, then the system is grounded right? Could I then attach two class 1 appliances without using an RCD?
Many quality Inverter Mfg. include GFCI/RCD inside of their units.
There seems to be some misunderstanding here.
I'm no expert in this but didn't JW say not to connect these devices to the house ground as in the case of a fault at the house the earth connection could carry the fault current into your equipment. I think a separate ground stake was the answer.
Is there any way to protect against shocks if running multiple mains appliances in a motorhome/campervan/etc where an earth electrode isn't practical?
IANAE, Probably not compliant with any standards but you could bond to any exposed metalwork/piping, thus "creating" your earth within your camper, however this would NOT be referenced to anywhere outside the camper, so caution needs to be exercised when touching something outside and inside the camper at the same time, such as stepping into and out of said campervan, or interacting with toll booths etc.
@Graham Parks,
As long as all of your internal bonding is good and you have a reliable RCD unit installed and tested.
Also if you're only using Class II appliances (with 2 pin plugs) this shouldn't be an issue as far as safety goes.
If you need any further advice, please ask.
@@mikeZL3XD7029 The common setup in smaller vehicles (especially self-build etc) is no earthing and no RCD when using the inverter. Sometimes these "installations" may have earth wires and RCDs, but as John mentioned in the video, they may not provide any protection.
@@deelkar Can you explain the tollbooth scenario? How do you get significant current flow via the inverter if the vehicle is otherwise isolated?
@@grahamparks8885 Sometimes people fit these "grounding straps" to their vehicles and forget. But yes, the scenario is a lot less likely to have a completed circuit than say, on a camping ground where stuff is maybe attached to the camper which could carry current, maybe there are other things touching the vehicle at that time that are grounded (Metal objects to warn you of oversize if you hit them etc.) Although far-fetched one has to consider these kinds of scenarios when dealing with earthing. The thing is to exclude classes of faults, not thinking of a couple of faults and then just avoiding those scenarios you thought of.
Hi John can u tell me what I need to do I want to install 4 sockets in a shed the shed is 20 metres away from the outside socket of my house can i just run cable from outside socket to shed and put the sockets on it???
So how would you deal with the earthing to the generator if it was to feed your normal house via a changeover switch within the property (or within the external meter cupboard) so that a secondary emergency supply could still be fed into the existing consumer unit? If the existing dwelling was TN-C-S earthing would it be acceptable to earth the generator into the TN-C-S earthing of the incoming supply so that all your existing RCD's within the consumer unit still worked? Just curious as a newbie 'prepper'.
I’d like to hear what JW thoughts on this is?
John you did not mention the ground screw on the case of the inverter that you were showing ? I take it that , that is where one would connect a grounding lead..?
Yes I was wondering the same thing. Also is the mains output earth connected to that? It that earth stud for earthing the battery or a ground spike.
ground spike
JW - could you make comment on the functionality of the case bondng terminal that was evident on the small 600w full sine wave inverter ?
I have repaired quite a few of those and most of them had the case connected to the PE terminal of the output socket. Perhaps the idea is to connect that to your water pipe or house earthing system in some way. It will still be an IT system, but as JW said, you should not connect more than one appliance to it anyway.
a lot of small generators and inverter use the PE terminal on the outlet to make an equipotential bonding conductor so if used for more than one item of class 1 equipment and a single fault occurs the exposed conductive parts on all of the equipment rises to the same potential, I would guess that the case earth terminal is connected to the PE terminal of the outlet and could be used to bond a metal chassis of a camper van, etc to make inside the vehicle an equipotential zone
The book IET Practitioner's Guide To Temporary Power Systems explains this in more detail
You can connect more than one pieces of equipment to an IT supply provided the following:
- They are all class 2
- If using class 1 equipment you must have an individual 30mA RCD protecting each item of equipment (not on the output of the generator as this will not provide any benefit)
- If supplying more than one item of Class 1 equipment the installation is required to be under the supervision of skilled or instructed people
@@marcuswareham1 But what about that case earth stud. What is it for?
Most car inverters have the ground of the socket connected to the negative 12/24V terminal,so it would be connected to the car metal frame.
I think this topic is more relevant than ever with recent power outage scares and people buying generators (battery ones too) and using suicide cables to backfeed etc.. and even some electricians don't consider floating neutrals, earth links, pme, ground rods etc...
Hello again does anyone know the answer to my question about the earth stud on the inverter that I asked previously. Nobody appears to know this. Thanks.
The other day I was reading 5v AC from a circuit with the RCBO turned off, does it need replacing?
What I actually did was turn the main switch off to get rid of the 5V and then sorted out the socket outlets that seemed to be suffering from damp rusty back-boxes. Replaced the back boxes for new and the flush socket outlets too for good measure. No the circuit is no longer tripping, but I'm still concerned about that 5V AC when the RCBO is turned off.
Probably capacitive coupling from adjacent cables. Very common where one circuit is switched off and the others are not.
I have a "cheapish" Giandel 12V to 240V inverter. In it's default state, it comes as IT. However, I wished to use it in a fixed install with RCDs so I bonded N to E (using a plugtop on one of the two outputs), and hammered a ground rod into the ground. I believe I have converted this IT system to TN-S.
While I don't have a Zs tester handy, i do have a megger RCD tester and the ADS times seem good.
Do you reckon I've done any bad things here?
No.
It's TN-S. The earth rod is just a reference to earth, so it doesn't need to be particularly low impedance, it's only there so any RCD will operate if a fault occurs between L and earth.
Loop impedance will depend on how much current the inverter can supply, which won't be very much.
Great videos as always full marks JW , I do believe I the centre tapped inverter generator type ,can find no continuity between n and E when not running ,is there a multimeter test for checking if its definitely a centre tapped version ,plugged into camper RCD trips on test ,hook up lead has earth wire that goes camper to generator 240 plug , ? Any tips on these centre tapped .
thanks for your effort.
Could you explain please how you would get a shock between two earthed appliances on the IT style inverter supply if one developed a live to earth fault? Surely this could only happen if the faulty appliance had no earth connection and you then touched another appliance that did have a good earth connection? The fault current would go from the inverter, through the live-earth faulty appliance, through you, into the second properly earthed appliance and back to the inverter thus completing the circuit? If all the class 1 appliances were properly earthed this would not be a problem as in the event of a live-earth fault in one appliance, all other class 1 appliances would be at the same potential and the fuse would blow? So using multiple class 1 items on an IT inverter supply to be dangerous needs both a live-earth fault to occur AND that faulty bit of class 1 equipment to have no earth connection?
2:02 If you connect two equipment you would have to use some kind of a splitter or a power strip. That would level the case potentials as if they had a failures that created the voltage between them that would blow the fuse.
well explained, would a grounding rod only be necessary if you plan to use your appliances outside or where ground contact is possible while using something? Im planning to use inverter off grid without any grid connection, I will be running everything through RCBO breakers though.
You MUST have an earth electrode for the installation, without it the RCDs / RCBOs won't work.
I would still be using ground conductors with all the wiring naturally, I suppose i should figure out where it needs to go then.
All the bigger generators I've workes with are TNC-S and marked as such?
I have a little inverter similar to the one you demonstrated, but designed for use in the US. It has a GFCI (RCD) outlet on it. Which obviously doesn't actually work. Not sure why they included it. I've never seen another inverter with that.
Another thing that applies specifically to North American larger generators: They're usually center tapped as you described, in order to provide both 120v and 240v supplies, typical to installations here. Those should always have the center tap referenced to ground/earth, as is standard practice in North America. Any 240v equipment intended for use here will be designed with that in mind, obviously. I haven't seen one here with one of the "hot legs" referenced to ground, but it wouldn't surprise me to see that on some cheap overseas unit not made to any actual standard.
Thank you John, I have been looking for some info on earthing my generator for some time now and you have hit the button. I have made a distribution panel which plugs into the 32A 230v output of my Champion 8kW generator with an RCD main switch to control 4x 16A mcbs to protect 4x 16A sockets on the distribution panel. At present with no earth electrode connected to the generator earthing terminal the RCD trips, can I assume by installing an earth electrode to the earth terminal of the generator this will solve the issue ? Regards Phil
If the RCD trips, then it's either connected incorrectly or whatever is connected to it has a fault. Adding an earth electrode will not change that.
Here in Norway we use 230V IT distrubution for mostly everything, such large transformers create high impedance to towards the ground, Isolated with a disneuter. Anywhere from 1A to 12A in fault current , which is kinda deadly because alot of times installations without RCD just floats around. So local grounding is importent for each installation
That power girs were also common in Russia,and all sockets were ungrounded.
Norway is an almost complete outlier in this respect. I believe French hospitals, at least in part, use IT systems as stray voltages referenced to ground are particularly deadly in operating theatres or anywhere else intrusive procedures are carried out. However, that's only safe where rigorous control over the entire electrical system and devices attached is possible, which is precisely what can't be guaranteed in a public distribution system.
For the record, such IT system with fully floating outputs were common back in the early days of electrical distribution, and it was only gradually learnt that it was essentially impossible to stop earth references appearing, even if these were via relatively high impedance.
Hello John! Some years back I was involved in helping with outdoor events as a marshal. We often had access to a modified bus, with seats removed, a kitchen and other work spaces, to use as the event command and control point. It had a built in mains generator, and the electrician who looked after it would earth it by wetting an area of ground with (I think) salt water, placing a large metal plate over that, and reversing the bus onto it to force about 14 tons of contact (or the equivalent of a pair of rear tyres, so maybe a only quarter of that).
We never had any issues, and the electrician always seemed very competent (I think he'd been a marine electrician). Do you believe this would have been a suitable alternative to a deep-driven earth electrode?
Ok for temporary use, assuming the metal plate was out of an area that the public could access.
@@jwflame As I recollect the bus wheels pretty much covered it, and generally only event personnel were in the immediate area.
No. Absolutely not. How long would the area under the plate stay wet? How would you know? What was the electrode impedance? Was it even measured? I immagine not. There are very strict regulations regarding event supplies and this was definitely in contravention.
A very common set up for large truck mounted generating sets, where a rod can't be installed, like those often used in the film and TV sectors. A large copper plate with a cable back to the generator earth point and the truck is driven onto it.
Not where I've worked. And I've worked on some pretty big film sets.
How does this relate (assuming it does) to UPS's with multiple outputs? Yes they will only be active ordinarily for a short period of time but when they are, should they be considered Generators? I'm thinking of the big name brands out there with multiple sockets on them aimed at the SME/Home market and wondering what the earthing arrangements might be on them?
UPS have to be connected to the power supply earth, because in normal operation, mains energy goes to the output and therefore output is referenced to ground. If the mains supply goes off, and batteries keep supplying power, you still have that earth link from supply to the output.
What would be the sensible arrangement for caravaners with say a Honda type generator?
Is it possible that the metal body of the lamp post is grounded? But then as you mentioned, any earth fault there will introduce some voltage at the earth point and that voltage can be "passed" to the site generator.
In my country, most of lamp posts are grounded. Alongside the cable, there is grounding strip buried and all posts are connected. So the grounding is pretty good. And that passing of voltage to the site generator is very unlikely for low voltage grid/generator. Grounding area is significant, and 230V is not much tbh. Would be bad in case when like medium voltage line fell and touched that lamp post. But still, earth resistance of all posts grounded is pretty low, so that potential would be spread.
Just thinking on about this.
I'm wondering how there would be a different potential on the case two different class 1 machines, where their cases were bonded together by a floating earth conductor?
Good question. I think it's like this. The equipment with the fault on it will have its metal casing live. Because it's not referenced to earth but the cpcs are connected together, the casing of the other item of equipment will also be live. A conductor or resistor carrying no current drops no voltage. But electricity likes to go back to where it came from so if you touch both items of equipment at once or either item of equipment and the generator frame, you complete the circuit and the current flows through you.
Hi JW. I have a portable petrol generator I want to use in a lock up garage. It is a frame generator by Machine Mart. I saw the need for an earth spike so I have held back from using it until I have drilled the floor and installed. Thanks this video is a first step in using it. I believe you have a video on earth spikes so will check that out. Thanks for the info. I take it I have done the right thing to not use it without a spike?!!
if a towable site generator was run without the earth electrode (but still retained the internal N-E bond), the GFCI/RCD on the distro would trip under a line to equipment chassis fault, but not a line thru person to ground fault, correct?
06:45
Yes.
7:10 But if the earth is left floating - not connected to N or the Earth, when the live touched the person, there would be no circuit to cause them harm - which is why birds sit on 11kV wires without killing themselves.
I did a temporary supply off a generator yesterday and was struggling for 10mins why i couldn't get the rcd of the cabin to trip. Went over my connections, earth continuity, even rang a colleague for advice still didn't make sense, i was about to make a service call into the generator company until I realized I had the neutral and earth leads around the wrong way on my fluke! swapped the leads everything was fine and dandy!! 🤦♂️😂 Thank crunchie it was friday.
As always great information. In Australia portable generators that are not connected to household supply, are not required to be earthed using an earthing rod and is advised not to use any external earthing. Refer AS2790.
Yes, likewise in Canada. A low impedance PE wire will always be a more reliable pathway back to the tranformer ground stud, so a ground fault is much more likely to have enough current to trip a breaker.
Do you have any experience with Hybrid inverters? The problem there is, that on the inverting side, they are normally setup as IT, so as they typically are installed in domestic environments, the output must be turned into a TN-S within the main panel. But now they as well do have a AC in, where the grid is just passed through the device once the battery is flat. In a TN system, they will probably not make any problems, but how can this situation be solved when the service is a TT? Without a N-G bond you get a hot Neutral. Some inverters do have a built in programmable N-G bonding relay, which can activate when the inverter is in off-grid mode. But those devices are very rare. Is there a method, how to install such inverters in a home when different earthing methods would be required to have a safe setup?
An informative and helpful video, thanks for posting it. I recently purchased an inverter to power my central heating and was intrigued by your comment re gas boilers. Disappointingly, although the time clock, motorised valves, pump and fan ran, the gas valve failed to operate, so complete failure! I have thought this initial test may have failed because it was operating in IT mode and not referenced to earth. As this inverter will not support TNS operation, I've returned it. Are you able to expand upon your comment re "certain gas boilers" please? Thanks
Hi JW, great stuff as always, but here comes a little challenge ...House supply is single phase TNS with 1960s lead cable, roadside cable replaced at some time, so most likely being TNC-S now. Outbuilding 30m away from house which i made a TT supply for obvious reasons. 3 phase generator next to it to supply the big machines. sharing the TT earth.. If i want to feed the house from that generator via a transfer switch, i wonder what to do with the PE as i definitely want to keep the outbuilding TT at all times. Ground resistance to the house is well below 100 Ohm, already got some earth rods on the house PE as i am a radio ham. My current idea is just to make the Genset a '"sort of'" TT supply to the house as the actual ground resistance would be low enough for reliably tripping the generator RCD, so perfectly safe (in my opinion) ..... What's you thoughts on this ? .... Thanks, Mike
Could the transfer switch be 3 pole and switch all conductors including PE over to the generator supply and isolate the grid, So when switched to grid L & N and the TN-S/TN-C-S earth are connected to the house (and isolated from the garage as normal), but when the switches is switched to generator the L,N & PE from the grid are isolated and you are connected to the L & N from the generator then the PE can be connected to earth electrodes at the house and then you would have a TT set-up when switched to the generator, as the generators earth electrode is the first T and the houses electrode is the second T
It is important to ensure complete isolation of all conductors including PE on the side of the switch which is not being used. Also important to ensure you have a 100mA delayed RCD on the generator to provide fault protection and then 30mA RCDs on the circuits in the garage and house to provide additional protection as with the TT set-up the rod resistance is usually high so RCDs are needed to meet disconnection times.
@@marcuswareham1 As far as i am aware, you not allowed to switch the PE at all, because there is a risk that the switch is on fault and then you would have no protection at all. It also won't fit my requirement to keep the outbuilding TT all the times (longer story). The genset has a 100mA RCD and both consumer units have 30mA RCDs as well. Just to recap what i want to do,... Outbuilding has electrodes, house has electrodes (but is actually TNC), so imho, this fulfills the requirements of a TT supply, essentially the same what you would do with an electric car charge point, the only difference is that this would be a supply, instead of a socket., hope that makes sense.
@@dynoguy maybe adding another rod at the house end 🤔 got me thinking on that one lol.
DNO new regs coming out means all new builds will have an earthed mesh at the house if its tncs supply effectively creating a backup earthing arrangement should you get a broken PEN.
maybe you could build some kind of system to switch the earthing to make house TT on generation and have the TT also at the workshop end and then when you switch off the generator it disconnects the house TT earthing arrangement and of course by manually switching off the gen set it also disconnects the TT earthing arrangements carried over from the workshop 😳
failing that maybe make a earth leakage and relay setup so that when on gen set there's a relay with earth leakage that sends a stop signal to the gen set and fires a separate relay to switch back to the original house TNS arrangement.
this is most definitely a head scratching setup buddy 👌 👏 👍
my ideas are just half baked and in no way conclusive
otherwise other issue depending on load is the stress on 1phase of 3phase generation 🙄 😒 could damage gen long term with loads on 1phase only possibly.
What would be the purpose of some rather large isolating transformers on the 3phase supply at the incomer of a large panel feeding a building ? It would be a government type building.
Do you ever see centre tapped Earths out of the generator as you would from a work site transformer? Particularly at 110v for which it’s common. Although I guess it cause it’s own safety issues if neutral is no longer neutral as expected.
The word nuteral is unfortunately assumed to = 0v even though it seldom is.
So if the earth of the Inverter is not referenced why does it have an earth connection? I wanted to use one of these to power a lathe from a 12v battery. I checked for continuity between the metal parts of the lathe and the earth connection of the inverter. There was conntinuity so I deduced from that that the earth connector of the inverter is not just there to protect the inverter itself but also, in this case, the lathe. But I am still not sure whether I should connect the inverter via its earth connection and a cable to an electrode in my garden. As I understand it, if I did that and either the L or N wire in the lathe connected to the metal part of the lathe, then 110 volts would shot down the earth cable into my garden and up one of my legs and down the other. On the other hand if I don't connect the earth cable to an electrode in my garden and the same thing happens, but this time I touch the lathe, then 110v will shoot down my arm through my heart and into the ground. This is a real dilemma. What is the lesser of these two evils. Risk heart palpitations or opt for electrical castration ? Can anyone advise me? Until I hear from you I will only be using the lathe wearing rubber shoes and wearing surgical gloves. This is't a joke by the way. I really need advice. My inverter has two 230v sockets. Does that mean that earth is referenced after all?
I got a diesel engine in a boat. Alternator is a normal one AFAIK. It seems really complicated on what "earthing" is. :(
thank you
3:46 no. A ground is not required for the operation of an RCD.
Although we call them Ground Fault Circuit Interrupters (GFCI) in America, these devices measure the current differential between the two power conductors.
If electricity is 'leaking' from one wire and not making it back on the other wire, the device will trip on a low current level ( >30ma).
Many quality Inverter Mfg. include GFCI/RCD inside of their units.
I don't think they are entirely useless, even though they won't have much to work with as the return path through earth does not exist. This is exactly why we use isolation transformers! *IT is safer!*
Also, simply bonding the frames of two appliances with reach of each other will mitigate the theoretical & highly unlikely danger of two opposing shorts to ground.
I believe it is better to consider portable systems to be isolated and leave it at that. there may be other reasons for grounding however.
ALWAYS CHECK THE MANUFACTURERS' LITERATURE!
Hi John, could you kindly explain the system whereby on a motorhome(insulated on tyres), the earthing is done through the metal vehicle chassis, even with a 3000w 240v inverter !
There are no earth rods pushed into the tarmacadam when the vehicles are parked up, but the RCD on the distribution board still works with some 'bonding' inside the invereter (victron multiplus for reference) but i dont understand the logic of how it works without the earth rod to ground.
Would make a great video if you had the time. :-)
You have done a tremendous amount of very useful videos. Keep up the great work. Thanks
think the inveter has earth leakage detection inside i belive on that victron.
might be wrong but only waybif not is to have a sensing circuit to trip off if a certain amount of ma is detected like a PEN protector used in car chargers ??
The inverter in the video had an earth stud. Is this connected to the earth pin of the socket and should that stud be connected to an earth spike. Nobody seems to be offer an answer to this question.
earth spike but really depends inside how the manufacturer has specified.
I have to ground batteries lithium on the casing as the manufacturer specifies to the inveter even thou its just near touch voltage of 50.2v.
you would hope the earth pin is isolated inside and you put your own rod in unless there's a earth relay to switch to a pme supply TNCS earth when the inverter goes back to mains power if it has mains input 😉 and isn't just a dc input only inveter to make pure sine wave 🤔
had a look online some.people are using a switch over earthing relay to switch between
Thank you for another excellent educational video. I appreciate your time and effort in producing these. Consider a situation where you wish to run an inverter output into the house to run two class 1 items (pc with a metal cases for example). This is a non-grid connected solar system charging batteries with an attached inverter (similar to your example inverter). Assume the house is TN-C-S. Would it be safe to use the household earth? I confess to not understanding why 1 item with a fault is safe.
@ Keith Marsh,
No, this new system you're talking about would be a separately-derived system, to the mains system you already have had installed.
The idea of you using your household earth is wrong, you should never reference another system to your mains earthing system, because if there is a fault on your mains system there is a chance that you could end up with a rising-earth voltage situation that could damage anything else connected to it or create a
shock situation, without you even noticing, until someone touches something metallic.
@@mikeZL3XD7029 Thanks for your reply Mike. I infer an earth spike should be used for my inverter. Would I encounter a problem where a network cable went from my inverter run PC to a main's PC?
@@KeithMarsh2 it depends on the network type. Cat 5 cables are transformer coupled at each end and have no earth connection.
Shielded cables and cat 6 could connect your separate earth's, though true shields should only ever be connected at one end.
So for my understanding, with the inverter being IT, a single class 1 device with a fault, gives no return path to get a shock, as such there could be a fault without even realising. Add a second class 1 device, and if that too develops a fault, could mean a potential between the two devices if both are touched as once. As such, a single RCD from an IT supply won't give any protection, however if every class 1 device has it's own RCD, if a double fault should occur, at least one RCD should trip due to the imbalance, taking it back to a single fault. No issues with class 2 devices.
Could u link neutral and earth on an inverter then use an RCD?
Possibly - depends on whether the earth is connected to anything inside the inverter. Some might be a centre-tap output 115-0-115 rather than 0-230
That makes no sense - if you use ONE single device. You add an RCD, but give up the isolation. Nothing is getting better by adding the RCD. If you plan to use MULTIPLE devices, then it makes sense to build an TN (WITH earthing rod and RCD).
@@MP-ou7lb I think John got it
Would it be dangerous to bring an earth from a ground rod inside a house with the combined neutral and earth supply?
No, provided it's connected to the same earth terminal as the CNE supply.
John, you say it is only a reference electrode but the quality of that connection to earth will affect whether an RCD will operate correctly or not if someone carries a fault current to an earth bonded item, will it not?
Electrodes on event systems are tested very rigorously for this very reason. In urban locations it can indeed be a challenge to install an effective electrode and lampposts are routinely used as the least worst option. I don't approve but sometimes you have no other option.
In what case would it be dangerous to connect multiple devices to a IT system?
One device would need to have Phase to PE fault and the other device would need to have a N to PE fault. And the PE from one device or between the devices needs to have a fault.
So 3 faults before there is a shock hazard?
(with small IT systems like the low power inverter)
@@Bushcraft-xz6xd So yes 3 independent faults would need to occur simultaneously before multiple class 1 devices on a Inverter become a problem.
Your second case would not work. Since its IT system, if there is one P-E fault nothing hapens because N is not bonded to ground.
@@lambda7652 Ah yes you are right. Only live to neutral faults are dangerous as there is no earth path back to the inverter. I deleted my last comment as it was confusing and just repeating what you already said lol!
But thinking about this further , that same set of very rare simultaneous faults would still be dangerous on any other system that does have an earth? Even using an RCD, depending on the conditions it might not detect any leakage to the ground and you could still get zapped between the faulty devices?
So at what point are we worrying too much over a very rare set of fault circumstances using multiple class 1 appliances on an inverter? After all the set of faults needed (minimum of 3 seperate faults) using an inverter is only one less fault needed in a regular domestic electrical system to achieve the same shock potential?
In a well maintained system this set of faults will just never happen and its a case of you can never allow for every eventuallity? I wonder if anyone has ever got a shock from the scenario we are discussing or if it's just theoretical?
@@Bushcraft-xz6xd "that same set of very rare simultaneous faults would still be dangerous on any other system that does have an earth" Yes.
"using an inverter is only one less fault needed in a regular domestic electrical system to achieve the same shock potential? "
How so? In my mind the inverter (an IT system) is way saver and needs more simultaneous faults to become dangerous. (depending on what exact system you see as "regular domestic electrical system "
)
My question is how does the inverter can output 230v and 0 volt, why is it not the same output as in IT systems we use in Norway?. We use RCBO almost on every homes with IT systems in Norway 230v on two and three phase. Between any wires are live 230v to any other wire except to earth, than all wires measured to earth is about 130 volt each. Your video indicates that if one wire in IT systems shorted to ground it will makes it become TN. But if we measure one wire to ground it will be about 130 volt, not 230 volt or 0 volt, but i have never tested what happens if one wire is shorted to ground with low resistance. If IT is shorted it will become TT if i understand right. Only 14% of homes in Norway uses TN and therefore the french Renault Zoe can not charge because of that it is designed to work on TN only. In Norway Renault Zoe is therefore sold with IT to TN transformer. Connecting one wire to earth does not make it a TN system as far as i can understand. Is there a way of transforming IT to TN without replacing transformer if we keep 230 volt and not changing to 400v? Electrical company say it will be very expensive to replace IT with TN. Please make a video about IT i love your videos i always learn something new from you. Thank you.
What he said👍
If the N and E are linked together inside the generator, why is this not a TN-C-S system?
well that 'C' part is very short here :D Essentially you dont have access to that point where its TNC while pluggin appliance. You can tell its TNC-S or abbreviate to TNS so to speak.
5:50 The earth is NOT connected to neutral on my generator. The socket earth is connected to the earthing terminal of the generator.
'NOT' = ~1Mohm.
Neutral on mine is referenced to neutral only ! It is only the other end of the phase windings. The sockets earth is not connected to N.
That then would appear to be IT.
@@TheEulerID It's connected now ;)
Thinking about my earthing problems with PA equipment and small generators I've come to the conclusion a microphone is a class one device recently I came across not the cheapest of generators 230 V 110 V to ground live and neutral but no 110 V output just blue sockets
I see there is some point in putting a trip in even if there's no Earth steak with two Class 1 Devices and tying neutral and earth
I continually come across small solar inverter systems based on extension leads with no earth and occasionally close one equipment with interference capacitors connected to live and neutral to ground Some call these the death capacitors
My 200W inverter earth is connected to the PCB but not the chassis or anything else !
I've been searching for some light regarding generator earthing. Mine generates 186v on the line winding and 60v on the neutral winding. The earth is floating and not n-e linked as the touch voltage would be 60v. So running the generator in a van to use class 1 machines how do we use any protection. Additional protection is out the window, bond all metal and machine casings to the generator frame ? But its floating, so unless it sees over 32 amps it wont cut out. Run the machines via a consumer unit and mcbs ?
How you managed to measure 186V and 60V respectively?🤔
@@piratedprivacy9052 from the output terminals to the generator casing on line and neutral.
Sounds like those voltages are from capacitive or inductive coupling. There are multimeters which have a setting to measure voltage using a moderate input impedance in order to eliminate ghost readings.
@@westinthewest yes was thinking of ghost voltage, but when I neutral earth bonded the line raised to 196V and neutral dropped to 50v under load on a 2kw heater. I will test it next week with a friends multimeter which can detect ghost voltages. Just dont want to put 50V ac on the van body and cook the batteries or electronic components.
If you touch the wires coming out of the inverter Will I get electrocuted?
Depends on the circumstances. If it's not connected to Earth anywhere, no shock if touching only one of the output wires.
If you touch both of them, or it's referenced to Earth via something connected to it, then you will get a shock.
Touching any of the outputs is something to be avoided.
@@jwflame
thank you very much.
TT, TN-C-S, TN-S it's all French to me...
;-P
Don’t you mean Latin?
@@Roverturbo TN-C-S stands for "terre neutre combiné séparé" which is very French
@@deelkar the word terra meaning Earth originated from Latin
A metal water pipe would have been a better choice than the lamppost.
Everything is better than the lamp-post.
If the supply authority see your wire coming out of your house and connected to their lamp-post,
they may not even ask the question and then just lop it off.
No earthing for you sweet-heart.......
@@mikeZL3XD7029 A gas pipe is one of the few things worse than the lamp post, JW talked about that before though.
@@station240 If a PME fault does occur, and all the lamp posts, gas and water pipes within the fault area are affected by a rise in voltage, isn't it better if your generator installation rises to the same voltage so that anyone touching one your appliances whilst leaning on a lamp post, doesn't experience a difference in voltages.
I've seen a reference to a concept called 'PME Islands' in Guidance Note 8, and I think this would apply here - but as often happens with that particular book, I read the first paragraph and found it too confusing to continue.
JW puts another great vid on the tubes
Me : T-N-S-I-T = tints (countdown)
JW : it's Earthing arrangements
Me: close enough
That inverter's DC cables don't look like they're rated for 57A... Just sayin'.
There's an earth terminal on your inverter - is that connected to the mains earth socket on it ? Mine hasn't got an earth terminal.
Around 4:35 you say an RCD is useless - I disagree. It SHOULD be useless but if there was an earth fault, it then might work and prevent someone getting a nasty shock !
At 7:05 you prove this.
For an inverter without a earth return path the only possible path is line to neutral which the rcd won't notice.
@@conorlanders8401 I don't use an RCD on the inverter anyway !
It seems to me that any RCD is useless unless there is a fault. Just as a fire extinguisher is useless unless there is a fire.
If neither L or N are connected to the case of the appliance, and one or other of them is connected to the case by a fault, that should present no risk, and not cause the RCD to trip, because the current will still go up the L and down the N, with none flowing to E. And nobody shocked.
If another appliance's simultaneous fault connects the other line to the "earth" that would trip an RCD. But then again, it'd probably trip an MCB or blow a fuse.
Its funny how everything in UK is "earth", even if it is a 12V vehicle system.
It's not just in the UK that it's called earth or ground in a vehicle, even if it is a misnomer. It's common terminology throughout the English speaking world. Really in such circumstances it ought to be called a "common", but I've long given up that fight. So all modern vehicles will be called "negative earth" whilst some much older vehicles were "positive earth", even if the chassis is not referenced to the ground at all.
@@TheEulerID Totally not. America uses "ground". Earth/protective ground only for AC mains. Its just funny saying "negative earth" when nothing is earthed.
@@Trancelebration Are you having trouble reading? The very first sentence said "It's not just in the UK that it's called earth or ground in a vehicle". I know in North Amercia the terminology is usually ground, which is why I put them in as equivalents. Whether it's called earth or ground is immaterial as the principle is the same.
Americans still refer to the common on vehicles as ground or earth.
This video seems to not distinguish a generator in complete isolation - as the ONLY source - from a backup generator tied to the greater grid's earth copper.
At 1:45, the earth lug at lower right in the 600W inverter, determines if the unit operates in IT mode or otherwise. All generators are identical to the 600W inverter, unless the generator should internally tie the two, which is not the default. The one earth rod, at 5:30, in an non-grid environment is more likely to decrease safety, than increase it.
Stand alone generators, in complete isolation, as the *ONLY* source of power, is not the same as a backup generator commonly connected via a transfer switch to the greater grid. The latter configuration automatically "exposes" the generator to potential anomalies from within a larger radius. Whereas, the former operates within a small self contained bubble. In either case the addition of an earth rod provides zero benefit relative to an RCD. Pick ANY realistic ohmic value for the earth rod and apply V=IR, even a 10mA RCD serves no purpose. ruclips.net/video/iyeGqyq9kXE/видео.html.
In this context, the only difference between a TN-S and a TN-C-S earthing system is the distance between the E-N bond point and the secondary, with the secondary typically connected to many interconnected rods, up and down the poles. With an isolated generator the distance between the secondary and the E-N bond is zero. An isolated power source is no different over dirt, than floating over water, or in flight. Adding an earth rod marginally increases risk.
All 2-pronged appliances operate in isolation. The only reason to bond E-N, *ONLY* at an isolated generator, is for 3-pronged appliances; that E-N bond is both necessary and sufficient.
~~~~~~~~~~~~~~~
Separately, at 9:00, referencing the center tap creates the North American scheme.
12:00 Page 26 OSG "Where more than one item of class I equipment is to be supplied by a [single phase???] generator, it is important that the earth connections of the socket outlets are connected to the neutral..."
WHY - and why specify single phase ?
Am I missing something here (go on, say it, 'brain cells' - LOL) ?
I don't see that connecting E to N has any benefit. I don't see that connecting E to the earth has any benefit either. Like I have, assume a floating earth circuit - it's not an 'earth' but simply equipotential bonding - 2 or more bits of earthed equipment will all be at the same potential - so what's the problem - asks the bird sitting on a 11kV line. The health risk is only from the power conductors.
Now, let's say a fault occurs and the machine 1 chassis is by a fault connected to line voltage. We have the bird on the live wire situation - with floating earth - so no issue. So now let's add a further fault on equipment 2 - connecting a power wire to the chassis of that machine. If it's the same wire as the first machine fault, there's no change. If it's another wire, it'll trip the overload protection. Either way, it's not adding danger.
So now let's go third situation - where the unearthed generator is sitting in a puddle on the ground - so is now earthed - so now if there's a fault, the RCD would trip. So it's still safe.
Are they inventing fake danger ? Any current >30mA not flowing through the permitted wires will trip the RCD. It won't matter what potential 'earth' actually is as there's no circuit.
I'd also like to know the answer to this question. It seems to me that you are correct, but perhaps there is something you and I have missed.
Hello can you help me connect a device that protects home appliances from high and low power supply I hope you help me and I am grateful to you....... One of the participants in your channel is your follower from Iraq
Now we know JW is actually onto something when he just simply calls earth "IT".
IT NEEDS FIXING.... Well thanks JW, now we know!
Um, that's not how an American residential transformer works. Your center tap is Neutral which is grounded. Each end of the coil will be 120 volts out of phase with each other. It's usually called something like Hot A and Hot B which are 180 degrees out of phase with each other. For 120 volts, you take one outer leg of the coil and use it with the center tapped Neutral. For 240 volts, you just use the outer legs of the coil. Here in America, 240 is typically used for major appliances like a range (cooker), water heater, or air conditioner. HotA(120V) - Neutral(0V) - HotB(120V)
a) We know.
b) Who cares? That's nothing to do with what John's talking about.
@@richij Regarding your point B,...you should actually care as this is exactly what JW explained with the cheap little Gensets having a blue and yellow socket, Most of them are wired exactly like the Americans do it.
an American residential system it's known as a split phase.
Cuz leg A and leg B make up one winding. With a center tap for neutral and Earth bonding.
wouldn't there be an issue with the fact of the generator producing a frequency of 60 hertz and not 50 hertz which UK electronics run on.
@@jonathanfurtado3696 Gee really?
JW, doesn't tend to focus on the electricity systems from the Third World, like the US.
@@jonathanfurtado3696 Generators are built to run at the same frequency as the mains supply in the country in which they are intended to be used.
The frequency has no bearing on the earthing system though.
Funny, when I learned to be an electrician I was told IT stood for impedance terra.
& that other generator system is clearly TNCS.
The more I watch these videos the more I wonder what your credentials are (if you actually have any).
The "I" refers to Isolé (french for isolated) It it sometimes referred to as high Impedance, which is where your having learned impedance comes from. I, as an ex electricity board electrician would suspect John has been either an installation inspector or an engineer. I might be wrong though. It is unfortunately true that two electricians/engineers often have three different opinions
@@gillywild to me, a totally isolated system has no T (t obviously being Terra or earth).
There certainly are impedance earthing systems that are often associated with generators.
I think, like many RUclips videos, the information in these needs taking with a pinch of salt. I’ve unsubscribed from John’s channel, this isn’t the first case of poor information I’ve seen on them sadly (not necessarily incorrect, but in my opinion poor).
I used a dual voltage genny 110v/230v and we were only allowed to use 110v power tools (before batteries tool days) back in the 80s.
I used a long cold chisel for an earth rod, it worked but when the arsehole site agent saw it he threatened to kick us of site if we didn't put a copper one in.
Copper does have MUCH better conductivity than steel. Steel might have done the job - but would need confirmation by measuring. As would copper, come to that.
@Tiny Tony Maloney,
Of course you did do that......
So someone trying to keep you safe is an arsehole....
What a prick you are.
surprising your only an electrician your too brainy i expect your much more
Funnily enough, most generators I’ve seen are unbounded internally. I guess since they lack RCD protection IT is presumed to be safer. The offshore arrangement with bonding the center tap is probably borrowed from the American residential 2 phase systems, where they really supply 240 V and bond the center tap to make sure that neither phase is more than 120 V over earth.